1. Field of the Invention
The present invention relates to an outboard motor including an internal combustion engine having a combustion chamber or chambers and provided with an intake silencer for reducing intake noise.
2. Description of the Related Art
A known outboard motor disclosed in, for example JP 2002-235621 A or JP 5-286490 A includes an intake silencer disposed in an engine compartment formed by an engine cover.
When an outboard motor including an internal combustion engine is provided with a single intake silencer, intake noise resulting from the pulsation of intake air taken in by the internal combustion engine cannot be satisfactorily and effectively reduced. Intake noise may be satisfactorily and effectively reduced if the outboard motor is provided with a plurality of intake silencers. However, the plurality of intake silencers simply incorporated into the outboard motor increase the size of the outboard motor.
A known outboard motor disclosed in, for example JP5-286490A, JP 2006-151242A or U.S. Pat. No. 3,610,198 includes an internal combustion engine provided with an intake system for carrying intake air for combustion into a combustion chamber or chambers, an engine cover forming an engine compartment in which the internal combustion engine is placed, a top cover covering the engine cover from above. In this outboard motor, intake air taken into an air-intake space defined by the engine cover and the top cover is carried into the intake system disposed in the engine compartment. Water that has entered the air-intake space is restrained from flowing into the intake system together with intake air.
When the intake system of the outboard motor placed in the engine compartment opens into the air-intake space outside the engine compartment, intake air taken into the intake system is of a temperature lower than the temperature of intake air taken into the engine compartment and heated by heat radiated from the internal combustion engine. The internal combustion engine can thus be charged at high charging efficiency and the internal combustion engine can achieve high output performance and lower temperature intake air is taken into the intake system.
However, when the intake system opens into the air-intake space outside the engine compartment, the intake pulsation caused by the internal combustion engine is transmitted through the intake system to the air-intake space. Since the air-intake space is defined by the top cover and the engine cover, the engine cover is vibrated by the intake pulsation transmitted to the air-intake space to generate noise.
In the known outboard motor referred to above, the intake system is provided with a water-stopping member for restraining water that has entered the air-intake space together with intake air from flowing into the intake system together with intake air.
In this known outboard motor, the air-intake opening and the intake system are connected by a labyrinthine air-intake passage to prevent water from mixing in intake air. However, the labyrinthine air-intake passage increases intake resistance, which deteriorates the output performance of the internal combustion engine.